Biochem 2.2 : Protein Structure Levels
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Questions and Answers

What is the significance of a protein adopting its correct tertiary structure?

  • It ensures that all amino acids are exposed to water.
  • It prevents the protein from interacting with other molecules.
  • It allows the protein to become a monomeric protein.
  • It enables the protein to function properly. (correct)

    • Which interaction type contributes to the stability of a protein's tertiary structure through noncovalent means?

  • Hydrogen bonds between nonpolar groups.
  • Ionic interactions between similarly charged groups.
  • Salt bridges between oppositely charged ionic groups. (correct)
  • Disulfide bonds formed between identical amino acids.

    • What happens to hydrophobic residues when a protein achieves its most energetically favorable conformation?

  • They form disulfide bonds with neighboring residues.
  • They transform into hydrophilic residues.
  • They are exposed to the external environment.
  • They are buried in the interior of the protein. (correct)

    • Why do disulfide bonds form in some proteins but not generally in cytosolic proteins?

    <p>Cytosolic proteins usually have a high concentration of reducing agents. (C)</p> Signup and view all the answers

    Which type of environment allows for the formation of disulfide bonds in proteins?

    <p>An oxidizing environment. (B)</p> Signup and view all the answers

    What is the term used for a polypeptide that consists of more than 50 amino acid residues?

    <p>Protein (D)</p> Signup and view all the answers

    Which type of bond links amino acid residues in primary protein structure?

    <p>Peptide bonds (B)</p> Signup and view all the answers

    Which of the following factors can alter the primary structure of a protein?

    <p>Mutations in the corresponding gene (D)</p> Signup and view all the answers

    What is the average molecular weight of an amino acid residue in a protein?

    <p>110 Da (D)</p> Signup and view all the answers

    If a protein has a molecular mass of 60 kDa, approximately how many amino acid residues does it contain?

    <p>600 residues (D)</p> Signup and view all the answers

    What is one consequence of amino acids being noncovalently bonded in polypeptides?

    <p>They enable the formation of various protein structures (D)</p> Signup and view all the answers

    What distinguishes tertiary structure from secondary structure in proteins?

    <p>Tertiary structure refers to the overall 3D conformation (C)</p> Signup and view all the answers

    What determines the higher levels of protein structure such as secondary, tertiary, and quaternary?

    <p>The primary structure of the protein (D)</p> Signup and view all the answers

    Which type of interaction is responsible for the formation of secondary protein structures?

    <p>Hydrogen bonds between backbone groups (A)</p> Signup and view all the answers

    What is the role of peptide bond rotation in protein folding?

    <p>It does not allow free rotation and limits conformations (A)</p> Signup and view all the answers

    What is the characteristic of an α-helix structure in proteins?

    <p>The backbone coils with hydrogen bonding every four residues (D)</p> Signup and view all the answers

    What type of protein structure is characterized by extended strands and sheets?

    <p>β-sheet (B)</p> Signup and view all the answers

    What does primary structure determine about a protein's folding?

    <p>It determines which interactions are favorable or unfavorable (C)</p> Signup and view all the answers

    What must happen for distant oppositely charged residues to interact?

    <p>A conformation must bring them into proximity (C)</p> Signup and view all the answers

    What structural feature is primarily responsible for protein's stability in aqueous solution?

    <p>Hydrophobic Effect (C)</p> Signup and view all the answers

    Which of the following concepts was proposed by Linus Pauling regarding protein structure?

    <p>Various conformations may arise from peptide backbone constraints (C)</p> Signup and view all the answers

    What primary force is responsible for holding α-helices together?

    <p>Hydrogen bonds between backbone functional groups (C)</p> Signup and view all the answers

    Which amino acid is commonly found in α-helices due to its size?

    <p>Glycine (B)</p> Signup and view all the answers

    What structural problem does proline create in α-helices?

    <p>Proline introduces kinks that destabilize the helix (D)</p> Signup and view all the answers

    What are the two configurations that adjacent β-strands can take in a β-sheet?

    <p>Parallel and Antiparallel (B)</p> Signup and view all the answers

    What type of turn is involved in linking adjacent antiparallel β-strands?

    <p>Beta-turn (D)</p> Signup and view all the answers

    Why does glycine tend to disrupt α-helix formation?

    <p>It allows for too much flexibility due to its small side chain. (D)</p> Signup and view all the answers

    What stabilizes adjacent β-strands in a β-sheet?

    <p>Hydrogen bonds between N-H and C=O groups (A)</p> Signup and view all the answers

    How many amino acids typically comprise a β-turn connecting β-strands?

    <p>Four amino acids (B)</p> Signup and view all the answers

    What effect does proline's structure have on its ability to participate in hydrogen bonding?

    <p>Proline has no hydrogen atom bonded to its nitrogen, limiting bonding. (B)</p> Signup and view all the answers

    What is the primary difference in stability between parallel and antiparallel β-strands?

    <p>Antiparallel strands provide stronger hydrogen bonding (A)</p> Signup and view all the answers

    What role do glycine and proline play in β-turns?

    <p>They facilitate the sharp turn because glycine is flexible and proline can form cis peptide bonds. (C)</p> Signup and view all the answers

    Which statement is true about parallel strands in β-sheets?

    <p>They have their C-terminal ends aligned but require longer connections. (B)</p> Signup and view all the answers

    What is a characteristic feature of adjacent strands within a β-sheet?

    <p>They may comprise segments that include unstructured regions or α-helices. (C)</p> Signup and view all the answers

    How can β-sheets be further stabilized?

    <p>By favorable interactions such as ionic interactions or hydrogen bonding. (B)</p> Signup and view all the answers

    What defines the tertiary structure of a polypeptide?

    <p>It is the three-dimensional folded form known as the native structure. (C)</p> Signup and view all the answers

    Which of the following statements about a β-sheet is false?

    <p>The connections between strands can alter their relative orientation. (C)</p> Signup and view all the answers

    What determines a protein's biological functions?

    <p>The ability to adopt a specific folded shape. (C)</p> Signup and view all the answers

    What is essential for the formation of β-turns?

    <p>Flexibility provided by residues like glycine and the ability of proline to form cis peptide bonds. (D)</p> Signup and view all the answers

    Which structural features can occur in the same β-sheet?

    <p>A combination of parallel and antiparallel strands can exist. (B)</p> Signup and view all the answers

    Study Notes

    Protein Structure Levels

    • Proteins are chains of amino acids (peptides)
    • Chains with >50 residues are polypeptides
    • Interactions between distant residues create structure levels (primary, secondary, tertiary, quaternary)
    • Primary: Amino acid sequence maintained by peptide bonds
    • Secondary: Hydrogen bonds between backbone atoms create coils (alpha-helices) or sheets (beta-sheets)
    • Tertiary: 3D shape resulting from interactions of side chains (hydrophobic effect, hydrogen bonds, disulfide bonds etc)
    • Quaternary: Multiple polypeptide subunits (subunits) bond together

    Primary Structure

    • Amino acid sequence determines the protein's 3D shape
    • Sequence determined by gene (Biology Chapter 2)
    • Primary changes can alter overall structure
    • Average amino acid residue molecular weight ~110 Da (0.11 kDa)
    • Molecular weight estimates amino acid counts

    Secondary Structure

    • Alpha-helices: Coils stabilized by hydrogen bonds between backbone atoms 4 residues apart
    • Beta-sheets: Sheets stabilized by hydrogen bonds between adjacent strands
    • Glycine and proline can disrupt alpha-helices
    • Side chain interactions can stabilize or destabilize secondary structures

    Tertiary Structure

    • 3D shape resulting from various interactions
    • Hydrophobic residues cluster inside the protein
    • Non-covalent bonds (hydrogen bonds, salt bridges)
    • Covalent bonds (disulfide bonds)
    • Stabilization factors determine the structure

    Quaternary Structure

    • Multiple polypeptide chains (subunits) bond
    • Hydrophobic interactions stabilize subunits' interactions
    • Can be homo- or hetero- (identical or different subunits)
    • Subunits: dimers, trimers, tetramer or oligomers/multimers
    • Individual subunits fold to form tertiary structure independently

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    Biochemistry 2.2 Protein Structure PDF

    Description

    Test your knowledge on the different levels of protein structure, including primary, secondary, tertiary, and quaternary structures. This quiz will explore how amino acid sequences influence the 3D shape of proteins and the interactions that stabilize these structures.

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